| 摘要 |
<PICT:0956650/C1/1> A continuous process for the preparation of NH4F.HF comprises the steps of (1) heating an aqueous solution of NH4FHF and NH4F to expel NH3; (2) removing part of the NH4FHF-enriched solution, cooling it and separating crystallized NH4FHF from the mother liquor; (3) recycling the mother liquor to step (1); and (4) supplying additional NH4F to step (1). As in the flow diagram, NH4F solution, 7, of 3-30% concentration, preferably 15-30%, which may be prepared by neutralizing commercial fluosilicic acid with ammonia, is mixed with recovered mother liquor from line 8 in evaporator 1, and maintained at a constant temperature between 120 DEG and 140 DEG C., preferably between 130 DEG and 132 DEG C., the rate of mixing such that the fluoride concentration is maintained constant at e.g. 50%, and the NH4F mol. fraction at e.g. 0.47. NH3 evaporated is dehumidified at 5, and reacted at 6, with fluosilicic acid. SiO2 is filtered off and NH4F solution recirculated to 1 by line 7. NH4FHF-enriched solution is removed continuously from 1, diluted with water and cooled, to give crystals of NH4FHF which are filtered off at 3 and dried in drier 4. The mother liquor is recycled by line 8. |
